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DIELECTRIC MEASUREMENTS OF A THERMAL DECOMPOSITION

ESTEL Lionel*, LEDOUX Alain, POLAERT Isabelle

Laboratoire des Risques Chimiques et Procédés, Institut National des Sciences Appliquées de Rouen, Place Emile Blondel, BP 8, 76131 Mont-Saint-Aignan Cedex

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^{*Corresponding author}

Abstract

2,4-Dinitrophenylhydrazine (Brady's reagent) is an important reagent related to hydrazine. As shown in figure 1, most aldehydes and ketones react very readily with this reagent to give 2,4-dinitrophenylhydrazones:

This chemical intermediate is present in many well known organic reactions. For example in the Barton vinyl iodine procedure [1] is a in which a hydrazone is converted in a vinyl iodide. In the Bamford-Stevens [2,3] reaction which is a chemical reaction whereby treatment of tosylhydrazones with a strong base gives alkenes.

The thermal activation of hydrazone can cause safety problems. The decomposition reaction is exothermic so that self-heating of the product increases its reactivity. Such a self-accelerating decomposition is accompanied by the formation of hot gaseous decomposition products which can lead to a thermal runaway. These hazardous events have to be avoided and appropriate precautions are to be taken. In the chemical industry, a key step for the assessment of thermal risk and runaway is the kinetic parameter estimation of such chemical reactions. The kinetic data are very often estimated by laboratory tests, which include many types of calorimetric instruments. As a rule a screening of the most hazardous chemicals is conducted. In the first step, the measured heat release curve gives the apparent activation energy level. In the second step, the characteristic behaviour of the decomposition reaction is observed with an isothermal measurement.

In a previous work [4], a new method for kinetic parameter estimation which is based on microwave dielectric measurements of chemicals has been developed. In this paper, a hydrazone reaction of decomposition is studied with an extended method using a network analyser for the real time measurement of dielectric properties.

References

1. Barton, D.H.R., O’Brien, R.E., Sternhell, S., J. Chem. Soc., pp. 470-476, 1962.

2. Bamford, W.R.; Stevens, T.S., J. Chem. Soc., pp. 4735, 1952.

3. Shapiro, R.H.; Org. React., 23, pp. 405-507, 1976.

4. Estel, L., Bonnet, C., Delmotte, M., Cosmao, J.M., ChERD, pp. 1212-1216, 2003.
Keywords : dielectric properties, kinetic parameter, hydrazone, chemical hazards, decomposition